It'd be excellent to have the ability to add additional buttons under the '+' group (or overall) to the Timeline control - similar to what can already be done with ribbons. This could be done to allow users trigger actions, open create forms, etc. via a control that is often central to most forms.

We've added custom connectors for customers (Use custom connectors with the timeline in Power Apps - Power Apps | Microsoft Learn) to allow data that would be otherwise impossible to show in the timeline which as significantly cut down the need for separate subgrids and controls (such as rolled-up activities from child records of a custom table + non-activity records).

Re: non-activity records, we wanted to avoid the security limitations of using activities while still giving users a streamlined experienced like the timeline offers. This works great with custom connectors, allowing users to see a complete/filterable chronology of interactions, but has one drawback in that we've had to use a custom ribbon button to support creating the record - not great UX.

Outside of the specific example I've given, there are certainly lots of other use-cases and benefits for implementing this and I hope it's considered.